1. Field of the Invention
The present invention relates to a valve device having a valve resting mechanism used for an internal combustion engine, and particularly to the valve device in which a valve lifter having a lost motion mechanism is interposed between a cam and a stem of a poppet valve.
2. Description of Background Art
With respect to an internal combustion engine of a type in which a plurality of intake valves or exhaust valves are provided in one cylinder, there is known a technique in which a valve resting mechanism is provided for at least one of the intake (exhaust) valves for holding the intake (exhaust) valve at the close position irrespective of operation of a cam. With this configuration, all of the intake (exhaust) valves are opened/closed in an intermediate/high intake amount operation region, for example, upon intermediate/high speed rotation or intermediate/high load operation of the internal combustion engine, and the valve having the valve resting mechanism is kept in the resting or closing state in a low intake amount operation region, for example, upon low speed rotation or low load operation of the engine.
A valve device having a valve resting mechanism has been disclosed, for example, in Japanese Patent Laid-open No. Hei 7-259520. This valve device is configured such that a valve lifter (tappet), which is interposed between a cam and a stem of a poppet valve, is usually biased by a (compressive) spring in the direction in which the valve lifter is engaged with the cam. A plunger (connecting member) is provided in the valve lifter in such a manner as to be slidable in the direction of a diameter of the valve lifter. The plunger is biased in one direction by a compressive spring provided in contact with one end of the plunger, and the other end of the plunger is received by a piston disposed coaxially with the plunger. The plunger has a hole in or from which the valve stem is movable.
When the piston is at the retreated position, even if the hole is aligned with the stem and the valve lifter is moved up and down by the cam, the stem is only moved in or from the hole and thereby the vertical motion of the valve lifter is not transmitted to the valve. To be more specific, the valve is kept at the close position irrespective of the motion of the cam by the lost motion mechanism composed of the plunger, piston and compressive spring. The piston is driven by a hydraulic pressure, and when the piston projects from the retreated position, the plunger is slid against the compressive spring and the hole is deviated from the stem, so that an upper end of the stem is locked with the plunger in a state being in contact with a lower surface of the plunger. Accordingly, the valve is driven by the cam via the valve lifter.
In the valve device of the type in which the lost motion mechanism in the valve lifter is driven by a hydraulic pressure, as shown in FIG. 7, a peripheral groove 03 for introducing the hydraulic pressure is generally formed in an inner peripheral surface of a valve lifter hole 02 for slidably guiding a valve lifter 01.
In FIG. 7, reference numeral 04 designates a plunger, and 05 is a compressive spring for biasing the plunger. A hydraulic pressure is directly applied to an end surface of the plunger 04 via an oil hole 06 provided in the valve lifter 01. The valve lifter 01 is biased upwardly by a valve lifter spring 07, but is pushed down by a cam 08.
The valve lifter 01 is assembled to an upper position of the stem 09 in a state before the cam shaft is assembled, that is, in a state in which the cam 08 is not present over the stem 09. Specifically, the valve lifter 01 is inserted from above into the valve lifter hole 02, and is placed on and supported by an upper end of the spring 07 which freely extends upwardly with its lower end supported by the cylinder head. Upon assembly of the cam shaft, the valve lifter 01 is pushed down by the cam 08, and is located at the position shown in FIG. 7 while compressing the spring 07.
In this way, the valve lifter 01 is initially placed on the freely extending spring 07, and accordingly, as shown in FIG. 8, a lower end 01a of the valve lifter 01 is located over a lower end 03a of the peripheral groove 03. As a result, when the valve lifter 01 is pushed down by the cam 08, as shown in FIG. 9, the valve lifter 01 is slightly tilted, and thereby the lower end 01a of the valve lifter 01 enters in the peripheral groove 03 and bits the lower end 03a thereof. This may obstruct the assembly of the valve lifter 01 from being smoothly performed.
In particular, the above inconvenience may easily occur if the assembling direction of the cam shaft is different from the extending direction of the valve stem, and in this case the assembly of the valve lifter must be performed with its tilting state corrected by means of a jig or the like. This complicates the step of assembling the valve lifter.
In view of the foregoing, the present invention has been made, and according to the present invention, there is provided a valve device having a valve resting mechanism used for an internal combustion engine, in which a valve lifter having a lost motion mechanism is interposed between a cam and a stem of a poppet valve. The valve lifter is usually biased by a spring in the direction in which the valve lifter is engaged with the cam. A peripheral groove, adapted to introduce hydraulic pressure for driving the lost motion mechanism, is formed in an inner peripheral surface of a valve lifter hole for slidably guiding the valve lifter. The valve lifter, the spring, and the peripheral groove are formed in such a manner that a lower end of the valve lifter is positioned under a lower end of the peripheral groove in a state in which the spring is freely extended.
According to the present invention, the lower end of the valve lifter supported on the freely extending spring is located below the lower end of the peripheral groove at the initial state of assembly of the valve lifter. With this configuration, when being pushed down by the cam upon assembly of the cam shaft, the valve lifter does not bite the peripheral groove. This makes it possible to smoothly assemble the valve lifter and the cam shaft.
The above function and effect are particularly advantageously and significantly achieved for the valve device of the present invention, which is characterized in that the assembling direction of the cam shaft is different from the extending direction of the valve stem.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description